Pulse width discriminator circuit



c. l... LONGMIRYE 2,585,803

PULSE WIDTH DISCRIMINATOR CIRCUIT Filed April 18, 1945 Feb. 12, 1952 FIG I f 33 32 38 BIASED 7| AMPLIFIER OUTPUT I as ADJUSTABLE 34 BIAS SOURCE L]; SQ? 1 .1

52 53 54 56 \A ea 5 491 491; 47 5a 6 GIS 70 7| INVENTOR.

CONRAD L. LONGMIRE ATTORNEY Patented F eb. 12, 1952 PULSE WIDTH DISCRIMINATOR CIRCUIT I Conrad L. Longmire, Boston, Mass, assignor, by mesne assignments, to the United States of America as represented by the Secretary of War Application April 18, 1945, Serial No. 588,992

5 Claims. 1

This invention relates to communication system and more particularly to circuits adapted to operate in response to signals of predetermined time duration and varying amplitude.

Communication systems have been devised in which it is possible to discriminate between signals of varying time duration. However, in operating these systems it has been found that the quality of discrimination is impaired where the amplitude of the signals fed to the discriminator circuits of the systems varies materially. The varying amplitude of the signals fed to these (11..- criminator circuits may be due to various reasons. For example, they may be due to the varying distance of the transmitters from the receivers in the systems, or the varying power used at the various transmitters.

One of the objects of the present invention, therefore, is. to provide pulse discrimination systems which will result in improved discrimination against signals of predetermined time duration and varying amplitude.

In accordance with the present invention there is provided a novel circuit which includes a source for supplying signals which may vary in time duration and also in amplitude.

nals are fed to a sawtooth generating means The source sigwhi'ch produces signals of an amplitude substantially proportional to the time duration of the source signals. Means are also providedfor passing signals of predetermined amplitude from the sawtooth generating means.

For a better understanding of the invention, together with other and further objects thereof,

reference is had to the following description taken in connection with the accompanying drawings.

In the accompanying drawings: Fig. l is a schematic diagram of a discriminator circuit employing the present invention; and

HI, which provides signals that may vary in amplitude and time duration,

Receiver 59 is connected to a cathode. I! of an electron tube it through a capacitor [3i The electron tube l2 may be a triode connected as a diodeas shown, or it may be any suitable diode 2 tube. The cathode H is connected to ground through a resistor 15. Plate i? of the electron tube I2 is connected to a control grid 18 of an electron tube [9. Electron tube 19 may be a pentode as shown, or it may be any other suit able electron tube having a control grid. Cathode 29 of tube I9 is connected to ground, and suppressor grid 22 is connected to the cathode 29. The control grid 18 is connected to ground through a resistor 23. A screen grid 24 of the electron tube 19 is connected to a suitable B+ voltage source through a resistor 25. The screen grid 24 is bypassed to ground through a capacity 21. Anode 28 of the tube 19 is connected to a suitable B+ voltage source through a resistor 29. The

, anode 28 is also connected to ground through capacitor 3i. The anode 29 of tube I9 is connected to biased amplifier 32 by means of a capacitor 33. An adjustable bias source 34 is connected by an isolating resistor 36 to the input 31 of the amplifier 32. An output may be obtained from the amplifier 32 at point 38. Amplitude-compensating means, comprising resistor 4!] and capacitor 4|, are connected from cathode ll of tube I2 to anode 28 of tube l9.

Referring now to Fig. 2, there is shown a series of Wave forms that may appear at various stages of the circuit illustrated in Fig. 1. These wave forms will be referred to in the description of the operation of the circuit of Fig. 1.

In the operation of the circuit of Fig. 1 it will be assumed that the compensating mean 40 and M are omitted. Signal 45 (Fig. 2), ,in this example a one microsecond pulse, is applied to the receiver It Wave form 46 (Fig. 2) shows the wave form of the pulse output of the receiver Hi. The wave form 46 is an integration of signal 25. The voltage represented by wave form 46 is applied through. tube !2 to the control grid I8 of tube IS. The dotted line 4! indicates the potential necessary to cause plate current cutofi in tube 19. Wave form 48 (Fig. 2) represents the voltage produced at anode 28 of the tube l9 when the voltage represented by wave form 46 is applied to grid I8. Wave form 48 is applied to the input 31 of amplifier 32. A dotted line 49 represents the minimum potential necessary at input 3! to produce an output at point 33. The level of the dotted line 49 is set by the bias source 38. Wave form 5! indicates that the output at point 38 is zero when wave form 48 is applied to input 3?.

If now, still assuming that compensating means 40 and 4| are omitted, a signal illustrated by wave form 52 (Fig. 2), also of one microsecond fore, will rise to a greater amplitude. This is illus- V trated by wave form 54 (Fig. 2). In this example it has been assumed that wave form 54 rises above line 49, and, therefore, the amplifier 32 has an output as illustrated by wave form 55. Since this circuit is a pulse width discriminator, no output should have been obtained at point 38 when wave form 52 was applied to receiver ID.

If now, still assuming that compensating means 40 and 4| are omitted, a signal illustrated by wave form 51, for example a two-microsecond pulse of the same amplitude as wave form 45, is applied to receiver It, the output of receiver H3 will be as shown by wave form 58 which is an integration of Wave form It will be noted that wave form 58 lies below line 41 for a longer time than either wave form 53 or G6. The voltage at anode 28 will, therefore, continue to rise as illustrated by wave form 59 to a point somewhat above the line 49. This will cause an output at point 38 as illustrated by wave form 6 i. It was desired to have the two-microsecond pulse produce an output at point 38.

However, with the compensating means M3 and M as an integral part of the circuits, the output at point 38 caused by wave form 52 will be eliminated without substantially affecting the output caused by Wave form 51. Thus, when wave form 45 is now applied to receiver ID, the voltage at anode 28 will be as illustrated by wave form 65. The initial drop in the wave form 65 is caused by the effect of wave form 56 being applied to anode 28 through the compensating means 4!] and 4|. Since wave form 65 lies entirely below line 49, the output at point 38 will be zero as illustrated by wave form $6. It will be seen that a similar drop in potential will occur at anode 28 when wave form 52 is applied to receiver Iii. The circuit is so designed that the drop in potential is sulficient to overcome the additional rise that was described in connecttion with wave form 54. This condition is illustrated by wave form 5?. It will be noted that wave form 6? lies entirely below line 49; therefore, the output at point 38 as illustrated by wave form 68 is zero. This is the desired condition. The drop in potential at anode 28 will still be present if Wave form 5! is applied to receiver it, but due to the fact that anode 28 rises in potential for a much greater period of time than was the case in either wave form 6? or 65, the potential at the input of amplifier 32 rises above the value necessary to give an output at point 38. Wave form "ill illustrates this fact in that the input 3'! of amplifier 32 rises above the critical potential illustrated by line 49, The output of amplifier 32 is shown by Wave form H.

It will be noted that compensating means 4!! and El avoided the output which would otherwise have been caused by the narrow pulse of high amplitude 52 but did not substantially affect the output caused by the wide pulse 51.

sates for the additional rise in potential at anode 28 caused by distortion of the input signal by dependent of the amplitude of the input pulse,

and will depend substantially upon the time duration of the pulse and the setting of the bias source While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention.

What is claimed is:

1. A translating circuit for signals of varying time duration and varying amplitude, comprising a normally conducting vacuum tube having at least cathode, anode and control grid electrodes, a condenser connected between said anode and cathode, a source of potential, a resistor connecting said source of potential to said anode, means to impress a first portion of said signals upon said control grid to render said vacuum tube nonconducting and to charge said condenser through said resistor, whereby sawtooth waves aregenerated substantially coincident with said source signals,a second resistor and a second condenser in series combination, said series combination bein coupled to a second portion of said source signals, means connected to said anode and to said series combination of said second resistor and said second condenser for combining said sawtooth waves and said source signals in phase opposition to produce resultant signals, and means for producing a signal when said resultant signals exceed a predetermined level.

2. The method of distinguishing pulse signals having greater than a predetermined duration from pulse signals having less than said duration and varying amplitudes comprising deriving from each pulse signal a sawtooth voltage signal substantially in coincidence therewith and having an amplitude varying directly with said signal duration, combining each pulse signal with the sawtooth voltage signal derived therefrom in opposition to derive resultant signals, and detecting resultant signals which are greater than a predetermined amplitude, whereby only pulses 0f longer than a given duration are distinguished.

3. A pulse width discriminator circuit comprising means for deriving integrated pulses from input square wave pulses of varying amplitudes and durations, a sawtooth generator coupled to said means and responsive to said integrated pulses for deriving from each of said integrated pulses a single sawtooth signal of substantially the same duration as said integrated pulse and substantially coincident with said integrated pulse whose amplitude is a function of the duration of said integrated pulse, a resistive-capacitive network connected to the first mentioned means, means coupled to said network and to said generator for combining each integrated pulse in opposition with the sawtooth signal derived therefrom, and means coupled to said last means for producing a signal when the output thereof ex-.

ceeds a predetermined voltage.

4. A pulse width discriminator circuit comprising means for integrating input square wave pulses of varying amplitudes and durations, a normally inoperative sawtooth voltage generator coupled to said means and responsive to said integrated pulses for deriving from each of said integrated pulses a single sawtooth signal of substantially the same duration as said integrated pulse and substantially coincident with said integrated pulse whose amplitude is a function 01 tioned means and to the output of said generator for combining each integrated pulse with the sawtooth signal derived therefrom in opposition, and means coupled to said last means for producing a signal when the output thereof exceeds a predetermined voltage.

5. A pulse width discriminator circuit comprising means for deriving integrated pulses from input square wave pulses of varying amplitudes and durations, means for deriving from each integrated pulse a single substantially linear sawtooth pulse having an amplitude that is proportional to the duration of said integrated pulse, means for combining at least a portion of each integrated pulse with the sawtooth pulse derived therefrom in opposition to produce a resultant pulse, and means for producing a signal when said resultant pulse exceeds a predetermined amplitude.

CONRAD L. LONGMIRE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,061,734 Kell Nov. 24, 1936 2,212,648 Pooh Aug. 27, 1940 2,250,708 Herz July 29, 1941 2,255,403 Wheeler Sept. 9, 1941 2,275,930 Torcheux Mar. 10, 1942 2,359,447 Seeley Oct. 3, 1944 2,391,776 Fredendall Dec. 25, 1945 2,412,485 Whitely Dec. 10, 1946 2,418,127 Labin Apr. 1, 1947 OTHER REFERENCES Ser. No. 464,750, De France (A. P. C.) published June 8, 1943. 

